1. Field of the Invention
The present invention provides an improved method for the preparation of esters such as t-butyl acetate.
2. Description of the Prior Art
It is known to produce esters by the reaction of an olefin such as isobutylene with a lower carboxylic acid over a sulfonate group-containing cation exchange resin. See U.S. Pat. No. 3,678,099 and the references disclosed therein including U.S. Pat. Nos. 2,678,332, 3,031,495, 3,172,905 and 3,173,943.
A problem which is encountered in such prior procedures has been the tendency for polymerization of the olefin to occur during the esterification which results both in significant yield losses and in the formation of products such as olefin dimer which are difficult to separate from the product ester. For example, isobutylene dimer forms an azeotrope with t-butyl acetate thus making separation exceedingly difficult.
Work has been performed with sulfuric acid as a catalyst. See, for example Pavlov et al., "GENERAL PREPARATIVE METHOD FOR THE ESTERIFICATION OF CARBOXYLIC ACIDS WITH ISOBUTYLENE IN THE PRESENCE OF TERT-BUTANOL", BULL soc. Chem Fr4. No. 12 P 2985-6 (1974). This reference describes the use of tertiary butanol in the sulfuric acid catalyzed system to suppress isobutylene polymerization. The sulfuric acid catalyst system has severe inherent difficulties associated with corrosion, problems of catalyst separation and recovery, and the tendency for side reactions.
U.S. Pat. No. 4,011,272 relates to a method for the production of tertiary butyl alcohol by reaction of isobutylene with water in the presence of a sulfonic acid resin and an organic acid such as acetic acid. Water is used in at least equimolar amount relative to the isobutylene and tertiary butyl alcohol is the primary product. The patent teaches that the minor amounts of tertiary butyl acetate which are formed can readily be hydrolyzed to form additional tertiary butyl alcohol.